1. Field of the Invention
The present invention relates to a control device of a gas sensor such as a contact combustion type hydrogen sensor to be mounted on a fuel cell vehicle.
2. Description of the Related Art
For example, conventionally, a solid polymer electrolyte fuel cell comprises a stack (hereinafter referred to as a fuel cell), which is constituted by stacking a plurality of cells on a cell formed by interposing a solid polymer electrolyte membrane between a fuel electrode and an oxygen electrode from both sides. Hydrogen is supplied as a fuel to the fuel electrode and air is supplied as an oxidizing agent to the oxygen electrode, and a hydrogen ion generated by a catalytic reaction at the fuel electrode passes through the solid polymer electrolyte membrane and moves to the oxygen electrode, and causes an electrochemical reaction to oxygen at the oxygen electrode, thereby generating a power.
Referring to a fuel cell such as the solid polymer electrolyte fuel cell, there has conventionally been known a protecting device comprising a hydrogen detector (a gas sensor) in a discharge system on an oxygen side of the fuel cell and serving to block the supply of a fuel when detecting that hydrogen on a fuel electrode side leaks toward the oxygen electrode side through a solid polymer electrolyte membrane by means of the hydrogen detector such as disclosed in JP-A-6-223850.
As for the hydrogen detector, moreover, there has been known a hydrogen detector of a gas contact combustion type which comprises a pair of a gas detecting unit formed of a catalyst such as platinum and a temperature compensating unit and serves to detect the concentration of a hydrogen gas depending on a difference in an electrical resistance generated together with the temperature compensating unit set in a relatively low temperature state such as an atmospheric temperature when the gas detecting unit is brought into a relatively high temperature state by heat generated through a combustion in the contact of hydrogen with the catalyst such as platinum.
In the gas sensor described above, the abnormal state of the gas sensor, for example, the presence of a short circuit is detected based on the detected value of the conducting current of each unit. For example, in the case in which the detected value of the conducting current is increased to exceed a predetermined decision threshold, it is determined that the short circuit is caused by an unrecoverable breakage generated on each unit or an abnormality generated on a circuit system, and the operation of the gas sensor is thus stopped.
In the fuel cell such as the solid polymer electrolyte fuel cell described above, however, water (humidifying water) is mixed with a reaction gas supplied to the fuel cell (for example, hydrogen or air) by means of a humidifier in order to maintain the ion conductivity of the solid polymer electrolyte membrane, and furthermore, reaction product water is generated by an electrochemical reaction during the operation of the fuel cell. For this reason, an exhaust gas of the fuel cell, particularly, an exhaust gas on an oxygen electrode side has a high wettability.
In the protecting device of the fuel cell according to an example of the conventional art, therefore, a dew condensation is generated on a hydrogen detector provided in the passage for an off-gas having a high wettability which is discharged from the fuel cell due to the off-gas in some cases. In some cases in which the hydrogen detector of a gas contact combustion type is particularly provided in a discharge system on the oxygen electrode side of the fuel cell, the detected value of an conducting current is increased to exceed a predetermined decision threshold due to a short circuit caused by the condensed water when the current conductance is carried out in a state in which the humidifying water or the reaction product water is stuck onto a gas detecting unit, and it is determined that an unrecoverable abnormality is generated on the gas sensor and the operation of the gas sensor is thus stopped even if the dew condensation is temporarily generated.